A number of coatings are known in this art. These coatings have been developed with different colors, varying degrees of corrosion resistance and relatively high amounts of trace elements which when in contact with the reactive steam, can affect the efficiency of the nuclear reaction.
Each generator normally receives two to three coats of primer prior to shipment to the plant site. Upon arrival at the plant site, generators are thereafter commonly stored outside without any further protection, typically for a period of time from three months to three years. During that time, rain and/or humidity cause present coatings to lose their intercoat adhesion and eventually cause the coatings to lose their adhesion to the substrate, which results in loss of corrosion protection. It is one purpose of this invention to provide extended corrosion protection in a primer.
The steam turbine generator industry requirement of a minimum of 200 hours salt fog resistance has not previously been met. Corrosion resistance is vital, in that any corrosion prior to installation requires expensive in-field refinishing, and extensive corrosion significantly shortens the service life of the generators. It is another purpose of this invention to provide a primer which meets the industry requirement of a minimum of 200 hours salt fog resistance.
Coatings known in the art prior to this invention have also failed to provide a primer with acceptable amounts of trace elements so as to avoid contamination of the reactive steam. The acceptable limits set by the industry on trace elements which have not previously been met are as follows:
______________________________________ PARTS PER MILLION BY ELEMENT WEIGHT OF WET PAINT ______________________________________ Chlorine 100 Cobalt 200 Fluorine 200 Lead 50 Sulfur 250 ______________________________________
Any greater amounts of trace elements in the primer coating the interior of the generators have been found to adversely affect the nuclear reaction, for the reactive steam which is circulated through the nuclear reactor comes in direct contact with the primer inside the generator. It is another purpose of this invention to provide a primer which contains limited trace elements within the acceptable industry limits.
One embodiment of the instant invention meets and exceeds all industry requirements described above in a single air dry waterborne system. Previously, two primers were needed, one for coating the exterior of the generator offering corrosion resistance, the other for coating the interior of the generator, which contained unacceptable amounts of trace elements.
Prior to this invention, no single product applicable on both the interior and exterior walls of the generators had been developed that met the industry standard and requirement of both environmental protection and limited trace element contamination. It is a primary purpose of this invention to provide such a single product to meet both industry requirements.